1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same, and, more particularly, to a zoom lens that is suitable, for example, for an image pickup apparatus using a solid-state image sensor such as a video camera, an electronic still camera, a broadcasting camera, and a monitoring camera or an image pickup apparatus such as a camera using a silver-halide film.
2. Description of the Related Art
A photographic optical system used for an image pickup apparatus using a solid-state image sensor requires a zoom lens having a high zoom ratio and high resolution. Further, an image stabilizing mechanism for compensating for a shake of an image generated when vibrations due to a camera shake is transferred to the zoom lens is required.
When an image stabilizing lens unit for image shake correction is moved in a direction perpendicular to an optical axis to correct an image shake, an aberration variation in image shake correction is required to be small and an excellent optical performance is required to be maintained during image stabilization.
For this reason, it is important to appropriately set a configuration of the entire lens or configurations of an image stabilizing lens unit and a lens unit disposed on the image side of the image stabilizing lens unit. For example, it becomes important to appropriately set a refractive power of an image stabilizing lens unit, a refractive power of a lens unit disposed on the image side of the image stabilizing lens unit, or an amount of movement during zooming. If the configurations are not set appropriately, it becomes very difficult to miniaturize an entire zoom lens, and maintain a high optical performance during image stabilization while securing a high zoom ratio.
Japanese Patent Application Laid-Open No. 2010-271362 discusses a zoom lens including first to fifth lens units having positive, negative, positive, negative, and positive refractive powers in order from an object side to an image side, in which an image shake correction is performed in a lens unit such as the fourth lens unit. U.S. Patent Application Publication No. 2011/0116174 and U.S. Pat. No. 7,889,438 discuss a zoom lens including first to fourth lens units having positive, negative, positive, and positive refractive powers in order from an object side to an image side, in which an image shake correction is performed in a lens unit such as the third lens unit.
In positive lead type zoom lenses discussed in Japanese Patent Application Laid-Open No. 2010-271362 and U.S. Patent Application Publication No. 2011/0116174, a zooming effect is mostly achieved as a first lens unit having a positive refractive power is moved toward an object side with respect to a second lens unit having a negative refractive power. During zooming, increasing the amount of forward movement of a first lens unit is advantageous to shortening a total lens length at a wide-angle end for determining the total lens length (a length from the first lens surface to the last lens surface), and to achieving high optical performance.
However, if the amount of forward movement of the first lens unit is large, a lens barrel having a length corresponding to the amount of forward movement needs to be stowed in the body. For this reason, the amount of forward movement of the first lens unit is limited by the total lens length depending on the specification, and thus a high zoom ratio is difficult to achieve and a study on a mechanical configuration for stepwise forward movement is required.